Perovskite nanocrystals have recently emerged as promising down-converters, due to their tunable emission wavelengths, narrow emission, non-scattering and high quantum yield (QY). These properties allow for improved LED performance by reducing losses associated with emission into the infrared, scattering to absorbing parts of the LED package, and down-conversion (i.e., low QY). One example is all-inorganic perovskite CsPbX3 (X=Cl, Br, I) nanocrystals, which have demonstrated many of the desired properties for down-converters in LEDs. However, perovskite nanocrystals have limited or no stability with respect to oxygen, organic solvents, and polar solvents such as water, which limits their application in LEDs as down-converters. Their instability in polar environments also makes it challenging to process the materials; for example, growth of a protection barrier following established methods for other nanoparticles can be difficult or impossible.